Housekeeping: fix some warning and docs

[tnull]

We fix how we expose ChannelId as it looked weird in docs and was reachable via multiple ways.

Moreover, we fix a bunch of compiler warnings.

[TheBlueMatt]

Oops, I had a few of these queued up in the first commit on #2169. Happy to rebase on here or whatever, though...I really need to stop slipping cleanups in PRs I think are gonna be merged soon (tm) :/

[valentinewallace]

I'm still getting 2 warnings on this branch, are those removable at this time?

[tnull]

Oops, I had a few of these queued up in the first commit on #2169. Happy to rebase on here or whatever, though...I really need to stop slipping cleanups in PRs I think are gonna be merged soon (tm) :/

Ah, did see that some of them were fixed there already. Now rebased after it was merged.

I'm still getting 2 warnings on this branch, are those removable at this time?

I addressed most of them now, only hesitant to touch the unused fn as_mut_ecdsa(&mut self) in type_resolver.rs as I'm not sure if it's meant to be used in a follow-up somewhere.

[TheBlueMatt]

I addressed most of them now, only hesitant to touch the unused fn as_mut_ecdsa(&mut self) in type_resolver.rs as I'm not sure if it's meant to be used in a follow-up somewhere.

It is, yes.

[tnull]

Force-pushed once more including the following fixups:

> git diff-tree -U2 2ece4dd0 411a3f7d
diff --git a/lightning/src/ln/monitor_tests.rs b/lightning/src/ln/monitor_tests.rs
index 95229348..ece24794 100644
--- a/lightning/src/ln/monitor_tests.rs
+++ b/lightning/src/ln/monitor_tests.rs
@@ -2232,5 +2232,5 @@ fn test_anchors_aggregated_revoked_htlc_tx() {
        let spendable_output_events = nodes[0].chain_monitor.chain_monitor.get_and_clear_pending_events();
        assert_eq!(spendable_output_events.len(), 2);
-       for (_idx, event) in spendable_output_events.iter().enumerate() {
+       for event in spendable_output_events.iter() {
                if let Event::SpendableOutputs { outputs, channel_id } = event {
                        assert_eq!(outputs.len(), 1);
diff --git a/lightning/src/util/test_utils.rs b/lightning/src/util/test_utils.rs
index 63b33a67..785b40be 100644
--- a/lightning/src/util/test_utils.rs
+++ b/lightning/src/util/test_utils.rs
@@ -283,5 +283,5 @@ struct JusticeTxData {
 }

-pub struct WatchtowerPersister {
+pub(crate) struct WatchtowerPersister {
        persister: TestPersister,
        /// Upon a new commitment_signed, we'll get a